JPH01236593A - High frequency heating device - Google Patents

Abstract

PURPOSE:To make the captioned device small, light, and low cost by providing a three-dimensional low-voltage winding to the transformer of a high frequency switching power circuit, and connecting the full-wave rectification-smoothing circuit, having the resistance restricting the current charging a smoothing capacitor, to the captioned winding to be a heater power source when a switching element is unconductive. CONSTITUTION:A three-dimensional low-voltage winding 19 is provided to a transformer 5 besides a primary winding 6 and a secondary high-voltage winding 7, a full-wave rectification circuit composed of diodes 20-23 is connected to the winding 19, a full-wave rectification-smoothing circuit 26 is composed with a smoothing capacitor 24 connected to the output side of the full-wave rectification circuit, and the heater of a magnetron 15 is connected to the circuit 26. And a current limitting resistance 25 is connected between the diode 22 of the full-wave rectification circuit and the winding 19. This enables the variation of a heater voltage, by the voltage variation in the third low-voltage winding of the transformer following the output variation in a high frequency switching power circuit, to be restrained in a fixed width, and thereby a device can be small, light, and low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-frequency heating device that supplies power to a magnetron using a high-frequency switching power circuit.

(Prior Art) Conventionally, as a high-frequency heating device that supplies power to a magnetron using a high-frequency switching power circuit, for example, there is a device having a configuration as shown in FIG. Are known.

Hereinafter, a conventional example will be explained based on FIG.

In the figure, 1 is a commercial AC power supply, 2 is a rectifying circuit, 3 is a capacitor, and 2.3 constitutes a rectifier-smoothing circuit 4, which obtains DC power from the commercial AC power supply 1.

5 is a transformer having a primary winding 6 and a secondary high voltage winding 7;
0 is a resonant capacitor, and 6.10 is connected in series to form a resonant circuit.

8 is a switching element, 9 is a free wheel diode, and is connected in parallel to the resonant capacitor lO.

The other end of the primary winding 6 and the other end of the resonant capacitor 10 are connected to the capacitor 3.

As described above, a high frequency switching power circuit is constructed.

Further, 12 is a high voltage capacitor, 13 and 14 are high voltage diodes, 12 to 14 constitute a half-wave voltage doubler rectifier circuit 1, which is connected to the secondary high voltage winding 7 of the transformer 5, and the switching element 8 is connected to the secondary high voltage winding 7 of the transformer 5. When conductive, high voltage DC power is supplied to the magnetron 15.

16 is a Peter transformer connected to a commercial AC power source 17 that supplies heater power for heating the cathode of the magnetron 15.

Further, a heating output control circuit 18 that controls power supplied to the magnetron 15 is connected to the switching element 8 .

A high-frequency heating device using a conventional high-frequency switching power circuit is configured as described above, and controls the heating output of the magnetron 15 by changing the ON time of the switching element 8 according to the output setting of the heating output control circuit 18. That's what I was doing.

(Problems to be Solved by the Invention) As described above, the conventional device has achieved high frequency by using a high frequency switching power circuit, but with this method, the magnetron heater power In order to keep constant,
Since commercial frequency power is supplied to the heater using a heater transformer, it is quite large and heavy.
There has been a problem in that it has not been possible to sufficiently reduce the size, purchase weight, and cost of equipment for the purpose of increasing the frequency.

The present invention was made to solve these problems, and an object of the present invention is to obtain a small, lightweight, and low-cost high-frequency heating device.

[Means to solve problems]

This invention provides a tertiary low-voltage winding in the transformer of the high-frequency switching power circuit instead of the heater transformer in the conventional device, and has a resistor in this to limit the current charging the smoothing capacitor when the switching element is non-conductive. A full-wave rectifier-smoothing circuit is connected to the heater power source.

[Effect]

With this configuration, fluctuations in the heater voltage due to voltage fluctuations in the tertiary low-voltage winding of the transformer due to fluctuations in the output of the high-frequency switching power circuit can be suppressed to a certain range, and the tertiary low-voltage winding can be used for the heater power supply. be able to.

〔Example〕

This invention will be explained below with reference to Examples.

FIG. 1 is a circuit diagram of a high frequency heating device which is an embodiment of the present invention.

In the figure, numerals 1 to 15.18 are the same as or equivalent to the conventional device shown in FIG. 5, and their explanation will be omitted.

In addition to the primary A-line 6 and secondary high-voltage winding 7, the transformer 5 includes:
A tertiary low voltage winding 19 is provided, and diodes 20 to
A full wave rectifier circuit consisting of 23 is connected, and a smoothing capacitor 24 is connected to the output side of the full wave rectifier circuit 2.
6 is constructed, and the heater of the magnetron 15 is connected to this.

In addition, the diode 22 of the full-wave rectifier circuit and the tertiary low voltage winding 1
A current limiting resistor 25 is connected between the terminals 9 and 9.

Next, the operation of this embodiment will be explained with reference to, in addition to FIG. 1, the current and voltage waveform diagrams of various parts shown in FIG. 2, and the output-filament voltage correlation diagram shown in FIG.

FIG. 2(a) shows the voltage on the primary side of the transformer 5.

Shows the relationship between currents. When a voltage 1 is applied in the forward direction between the pace emitters of the switching element 8, the switching element 8 is turned on, and the voltage 1 is applied to the primary wire 6 of the transformer 5. C is added, and the transformer primary current I□ flows as shown in FIG. At this time, the secondary high voltage winding 7 has ■N2=VD
A voltage of C (n21 n+ is the number of 2n■-order, primary windings) is added, and a high voltage of the sum of this vN2 and the voltage of the high-voltage capacitor 12 is applied to the magnetron 15.
The magnetron oscillates when the switching element 8 is turned on. At this time, flow 1. The part proportional to IN2 is transmitted to the secondary side, and the exciting part is stored in the transformer as it is, becoming residual energy.

Next, VBE is applied between the base and emitter of switching element 8.
When applied in the opposite direction, the switching element 8 turns off,
Due to the residual energy, resonance begins between the inductance viewed from the primary winding 6 side of the transformer 5 and the resonant capacitor 10, and a high resonant voltage with a polarity opposite to that when the transformer is on appears at VNI.

This resonant voltage is further boosted by the transformer 5, rectified by the diode 13, and charges the high voltage capacitor 12. At this time, since the high voltage diode 13 is conductive, a voltage close to zero is applied to the magnetron 15 via the diode 14, and the magnetron 15 is turned off.

Normally, in order to keep the loss of the switching element 8 small, the switching element 8 is turned on again when VCa becomes zero, so the off time Toff is determined by the resonance period, and the on time TON of the switching element is variable. As a result, the output of the magnetron is made variable. At this time, the switching frequency and this on time T. Voltage in case of N variable,
FIG. 2(b) shows the current. As shown in the figure, when the on-time ToN is changed, the current IN+ flowing through the primary winding 6 changes, and the supplied energy, lNlXVt1C, changes, so the energy supplied to the magnetron 15 also changes. Here, as shown in FIG. 3('a), the on-time T of the switching element 8. Between N and high frequency output,
Since there is a monotonically increasing relationship, the high frequency output can be arbitrarily controlled by controlling the on time TON or the switching frequency f.

In addition, the voltage applied to the tertiary low voltage winding 19 is shown in Figure 2 (
As shown in c), the number of turns of the switching element is 8), and the on time is T. It is constant regardless of N, and when it is off,
As can be seen from FIG. 2(b), the on time T. It increases or decreases depending on N. Therefore, if this waveform is directly subjected to full-wave rectification, the voltage will be dependent on the on-time TOH, as shown in Vf' in FIG. 2(C), but the current limiting resistor 25. By appropriately selecting the value of the smoothing capacitor 24, it is possible to suppress voltage fluctuations within a constant range, as shown in Vf in FIG. 2(C).

In the above embodiment, the resonant capacitor 10 is connected in series to the primary a-line 6 of the transformer 5, or the resonant capacitor 10 is connected to the primary winding 6 of the transformer 5 as shown in FIG.
Even if they are connected in parallel, the same functions and effects as in the above embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the heater power source can be obtained from the tertiary low voltage winding provided in the transformer of the high frequency switching power circuit, making it possible to reduce the size, weight, and cost of the device. Furthermore, since the magnetron heater voltage remains constant regardless of whether the output is high frequency output or low output, there is an effect that abnormal oscillation of the magnetron and generation of abnormal voltage can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a high-frequency heating device that is an embodiment of the present invention, FIGS. 2(a) to (C) are voltage and current waveform diagrams of the main parts of the device, and FIGS. 3(a) to (C) are d) is an output-filament voltage correlation diagram of the same device, FIG. 4 is a circuit diagram of another embodiment of the present invention, and FIG. 5 is a circuit diagram of a conventional example. In the figure, 1 is a commercial AC power supply, 4 is a rectifier-smoothing circuit, 5 is a transformer, 6 is its primary winding, 7 is a secondary high voltage winding, and 19 is a tertiary winding. 8 is a switching element, 9 is a freewheeling diode, 10 is a resonant capacitor, 11 is a half-wave voltage doubler rectifier circuit, 15 is a magnetron, 18 is a heating output control circuit, 25 is a current limiting resistor, and 26 is a full-wave rectifier-smoothing circuit. be. Note that the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A DC power source, a resonant circuit connected to the DC power source and consisting of a series or parallel connection of a primary winding of a transformer and a resonant capacitor, a switching element with a free wheel diode that excites the resonant circuit, and the switching element. a heating output control circuit that drives the transformer, a secondary high-voltage winding of the transformer and a half-wave voltage doubler rectifier circuit connected to it, a tertiary low-voltage winding of the transformer and a full-wave rectifier-smoothing circuit connected to it; circuit, and an anode and a cathode on the output side of the half voltage doubler rectifier circuit,
A secondary high-voltage winding of the transformer is provided with a magnetron to which a heater is connected to the output side of the full-wave rectifier-smoothing circuit, and a secondary high-voltage winding of the transformer is provided so that a forward voltage is applied to the magnetron when the switching element is conductive. A wire, a half-wave voltage doubler rectifier circuit, and a magnetron are connected to each other, and the full-wave rectifier-smoothing circuit has a diode, a resistor, and a smoothing capacitor, and the current that charges the capacitor when the switching element is non-conducting is connected to the wire, the half-wave voltage doubler rectifier circuit, and the magnetron. A high frequency heating device characterized in that the high frequency heating device is connected so as to be limited by the resistance.